Knowledge Cartography for Controversies: The Iraq Debate

In analysing controversies and debates—which would include reviewing a literature in order to plan research, or assessing intelligence to formulate policy—there is no one worldview which can be mapped, for instance as a single, coherent concept map. The cartographic challenge is to show which facts are agreed and contested, and the different kinds of narrative links that use facts as evidence to define the nature of the problem, what to do about it, and why. We will use the debate around the invasion of Iraq to demonstrate the methodology of using a knowledge mapping tool to extract key ideas from source materials, in order to classify and connect them within and across a set of perspectives of interest to the analyst. We reflect on the value that this approach adds, and how it relates to other argument mapping approaches

Dynamic tensile necking: influence of specimen geometry and boundary conditions

This paper examines the effects of sample size and boundary conditions on the necking inception and development in dynamically stretched steel specimens. For that task, a coordinated systematic experimental&-numerical work on the dynamic tensile test has been conducted. Experiments were performed using a tensile Kolsky apparatus for impact velocities ranging from 10 to 40 m/s. Three different sample-gauge lengths &- 7, 30 and 50 mm &- were considered for which the cross section diameter is 3.4 mm. The experiments revealed that the specimens' ductility to fracture depends on strain rate and sample length. Furthermore it was observed that, for those specimens having gauge lengths of 30 and 50 mm, the necking location varies with impact velocity. Numerical simulations of the dynamic tensile tests were carried out in order to characterize the dynamics of neck inception and development. For each specimen calculated, three types of boundary conditions were used, all of which match the experimentally measured strain-rate. It was pointed out that, while boundary conditions hardly affect the calculated stress&-strain characteristics, they strongly affect the wave propagation dynamics in the specimen thus dictating the necking location.The researchers of the University Carlos III of Madridare indebted to the Comunidad Autónoma de Madrid (Project CCG10 UC3M/DPI 5596) and to the Ministerio de Ciencia e Innovación de España (Project DPI/2011 24068) for the financial support received which allowed conducting part of this work. D. Rittel acknowledges the support of Carlos III Univer sity with a Catedra de Excelencia funded by Banco Santan der during academic year 2011 2012

On the Taylor-Quinney coefficient in dynamically phase transforming materials. Application to 304 stainless steel

We present a thermodynamic scheme to capture the variability of the Taylor-Quinney coefficient in austenitic steels showing strain induced martensitic transformation at high strain rates. For that task, the constitutive description due to Zaera et al. (2012) has been extended to account for the heat sources involved in the temperature increase of the material. These are the latent heat released due to the exothermic character of the transformation and the heat dissipated due to austenite and martensite straining. Through a differential treatment of these dissipative terms, the Taylor-Quinney coefficient develops a direct connection with the martensitic transformation becoming stress, strain and strain rate dependent. The improved constitutive description sheds light on experimental results available in the literature reporting unusual (> 1) values for the Taylor-Quinney coefficient.The researchers of the University Carlos III of Madrid are indebted to the Comunidad Autónoma de Madrid (Project CCG10-UC3M/DPI-5596)) and to the Ministerio de Ciencia e Innovación de España (Project DPI/2011-24068) for the financial support received which allowed conducting part of this work. D. Rittel acknowledges the support of Carlos III University with a Cátedra de Excelencia funded by Banco Santander during academic year 2011–2012.Publicad

Necking evolution in dynamically stretched bars: new experimental and computational insights

This paper presents new results on dynamic neck evolution in steel bars of varying diameters. Dynamic tensile tests were carried out in a Kolsky apparatus using cylindrical steel specimens with various cross-section diameters ranging from 1.5 mm to 4 mm. A high speed digital camera was used to record the deformation of the specimen during the loading process. Video recording of the tests enabled accurate experimental measurements of the necking evolution, specifically its growth rate as a function of the diameter. The experiments show that increasing the specimen cross-section slows down the neck development. This behavior has been further investigated using two different kinds of numerical calculations: (1) axisymmetric finite element simulations and (2) one-dimensional finite difference computations.The authors of the University Carlos III of Madrid are indebted to the Ministerio de Economía y Competitividad de España (Projects DPI2014 57989-P and EUIN2015-62556) for the financial support which permitted to conduct part of this work.Publicad

Dynamic Necking of Notched Tensile Bars: An Experimental Study

The mechanics of necking inception in dynamically-stretched notched specimens have been investigated. For that task, a systematic experimental campaign of quasi-static and dynamic tensile tests on martensitic steel specimens has been conducted. Samples with and without notches have been considered. Unlike the quasi-static tests, the dynamically-tested notched samples revealed that, under certain loading conditions, flow localization may develop away from the groove. The experimental results presented in this investigation show that the presence of sharp geometrical imperfections in ductile materials subjected to dynamic loading does not necessarily dictate the necking and fracture locus.D. Rittel acknowledges the support of Carlos III University with a Cátedra de Excelencia funded by Banco Santander during academic year 2011–2012. The researchers of the University Carlos III of Madrid are indebted to the Ministerio de Ciencia e Innovación de España (Projects DPI/2011-24068 and DPI/2011-23191) for the financial support.Publicad

Finite element analysis of AISI 304 steel sheets subjected to dynamic tension: The effects of martensitic transformation and plastic strain development on flow localization

The paper presents a finite element study of the dynamic necking formation and energy absorption in AISI 304 steel sheets. The analysis emphasizes the effects of strain induced martensitic transformation (SIMT) and plastic strain development on flow localization and sample ductility. The material behavior is described by a constitutive model proposed by the authors which includes the SIMT at high strain rates. The process of martensitic transformation is alternatively switched on and off in the simulations in order to highlight its effect on the necking inception. Two different initial conditions have been applied: specimen at rest which is representative of a regular dynamic tensile test, and specimen with a prescribed initial velocity field in the gauge which minimizes longitudinal plastic wave propagation in the tensile specimen. Plastic waves are found to be responsible for a shift in the neck location, may also mask the actual constitutive performance of the material, hiding the expected increase in ductility and energy absorption linked to the improved strain hardening effect of martensitic transformation. On the contrary, initializing the velocity field leads to a symmetric necking pattern of the kind described in theoretical works, which reveals the actual material behavior. Finally the analysis shows that in absence of plastic waves, and under high loading rates, the SIMT may not further increase the material ductility.D. Rittel acknowledges the support of Carlos III University with a Cátedra de Excelencia funded by Banco Santander during academic year 2011-2012. The researchers of the University Carlos III of Madrid are indebted to the Comunidad Autónoma de Madrid (Project CCG10 UC3M/DPI 5596) and to the Ministerio de Ciencia e Innovación de España (Project DPI/2008 06408) for the financial support received which allowed conducting part of this work

An analysis of microstructural and thermal softening effects in dynamic necking

The competition between material and thermal induced destabilizing effects in dynamic shear loading has been previously addressed in detail using a fully numerical approach in Osovski et al. (2013). This paper presents an analytical solution to the related problem of dynamic tensile instability in a material that undergoes both twinning and dynamic recrystallization. A special prescription of the initial and loading conditions precludes wave propagation in the specimen which retains nevertheless its inertia. This allows for a clear separation of material versus structural effects on the investigated localization. The outcome of this analysis confirms the dominant role of microstructural softening in the lower strain-rate regime (of the order of 10(3) s(-1)), irrespective of the extent of prescribed thermal softening. By contrast, the high strain-rate regime is found to be dominated by inertia as a stabilizing factor, irrespective of the material's thermo-physical conditions, a result that goes along the predictions of Rodriguez-Martinez et al. (2013a) regarding dynamically expanding rings.The authors are indebted to the Ministerio de Ciencia e Innovación de España (Projects DPI/2011-24068 and DPI/2011-23191) for the financial support. D. Rittel acknowledges the support of University Carlos III of Madrid with a Cátedra de Excelencia funded by Banco Santander during academic year 2011-2012

Dynamic recrystallization and adiabatic shear localization

It has recently been reported that, in alloys exhibiting early dynamic recrystallization (DRX), the onset of adiabatic shear bands (ASB) is primarily related to microstructural transformations, instead of the commonly assumed thermal softening mechanism as shown by Rittel et al. (2006, 2008) and Osovski et al. (2012b). Further, the dominant role of microstructural softening in the necking process of dynamically stretching rods showing DRX has been verified using linear stability analysis and finite element simulations by Rodriguez-Martinez et al. (2014). With the aim of extending this coupled methodology to shear conditions, this paper presents an analytical solution to the related problem of ASB in a material that undergoes both twinning and dynamic recrystallization. A special prescription of the initial and loading conditions precludes wave propagation in the specimen which retains nevertheless its inertia, allowing for a clear separation of material versus structural effects on the localization process. A parametric study, performed on the constants of the constitutive model, permits the identification of their relative role in the onset of the dynamic instability. The main outcome of the analysis confirms the strong destabilizing effect played by the development of DRX, consistently with the former statement regarding ASB, and contributes to rationalize the observations of other authors.The authors are indebted to the Ministerio de Ciencia e Innovación de España (Projects DPI/2011-24068 and DPI/2011-23191) for the financial support.Publicad

Dynamic necking of notched tensile bars: an experimental study

The mechanics of necking inception in dynamically-stretched notched specimens have been investigated. For that task, a systematic experimental campaign of quasi-static and dynamic tensile tests on martensitic steel specimens has been conducted. Samples with and without notches have been considered. Unlike the quasi-static tests, the dynamically-tested notched samples revealed that, under certain loading conditions, flow localization may develop away from the groove. The experimental results presented in this investigation show that the presence of sharp geometrical imperfections in ductile materials subjected to dynamic loading does not necessarily dictate the necking and fracture locus.D. Rittel acknowledges the support of Carlos III University with a Cátedra de Excelencia funded by Banco Santander during academic year 2011-2012. The researchers of the University Carlos III of Madrid are indebted to the Ministerio de Ciencia e Innovación de España (Projects DPI/2011-24068 and DPI/2011-23191) for the financial suppor